The CPIO's contents are extracted and exist in KFS's structures. It is
unused at this point, and unlike the old KFS, it won't be used during
regular operation. The old KFS would use the CPIO as the backing store for
readpage().

This might trigger a couple bugs, since the allocator will be handing out
more data that isn't already zeroed. Perhaps there are other bugs with
memory being below _end (and below the boot allocator). That should be
fine though, just be careful.